Magnetic moment 2.83 BM is given by which of the following ions?

(At.nos. Ti = 22, Cr = 24, Mn = 25, Ni = 28)

Magnetic moment is given by $\mu =\sqrt{n(n+2)}\mathrm{B}.\mathrm{M}$ where  n =   no. of unpaired electrons 

$\text{ When }n=2\text{ , then }\mu =2.83\text{ B.M. }$

$\text{ For }{\mathrm{Ti}}^{3+}\left(3d^1\right),n=1;{\mathrm{Cr}}^{3+}\left(3d^3\right),n=3;{\mathrm{Ni}}^{2+}\left(3d^8\right)$

                                  $n=2;{\mathrm{Mn}}^{2+}\left(3d^5\right),n=5$

Hence, $N{i}^{2+}$has two unpaired electrons, with magnetic moment 2.83 B.M.